Azomethine direct dyes or reduced precursors of azomethine direct dyes obtained from 2-alkylresorcinols, and hair dyeing process using these dyes or precursors

ABSTRACT

The invention relates to the dyeing of keratin fibres using azomethine direct dyes or reduced precursors of azomethine direct dyes of formula (I) and (II) obtained from 2-amino-3-hydroxypyridine. The invention relates to a dye composition comprising at least one azomethine direct dye or a reduced precursor of an azomethine direct dye, to a process for dyeing keratin fibres, using the said composition, and to their uses in the dyeing of keratin fibres. This composition allows a particularly stable and fast coloration to be obtained.

The invention relates to the dyeing of keratin fibres using azomethine direct dyes or reduced precursors of azomethine direct dyes obtained from 2-amino-3-hydroxypyridine.

It is known practice to dye keratin fibres, and in particular the hair, with dye compositions containing direct dyes, according to a “direct dyeing” process.

The process conventionally used in direct dyeing consists in applying to keratin fibres direct dyes, or colouring molecules, which have affinity for the said fibres, leaving them to stand on the fibres, and then rinsing the fibres. The direct dyes used hitherto are nitrobenzene dyes, anthraquinones, nitropyridines, dyes of azo, xanthene, acridine or azine type or triarylmethanebenzene-based dyes.

Other dyes are obtained from oxidation bases and oxidation couplers, which, once condensed, are applied onto the hair. For example, in documents FR 233 036, FR 2 262 022, FR 2 262 024, U.S. Pat. No. 4,221,729 and FR 2 261 750, diphenylamines such as leuco derivatives of indophenols, of indoamine and of indoaniline are used either alone or in combination with other dyes in dye compositions. Other compounds corresponding to oxidized derivatives of leuco derivatives such as those described in documents FR 2 254 557 and FR 2 234 277 are also known for dyeing keratin fibres.

The colorations that result from direct dyeing are temporary or semi-permanent colorations, since the nature of the interactions that bind the direct dyes to the keratin fibre, and their desorption from the surface and/or the core of the fibre, are responsible for their poor dyeing power and their poor fastness with respect to washing or to perspiration. These direct dyes are also generally sensitive to the action of oxidizing agents such as hydrogen peroxide, which makes them generally unusable in lightening direct dye compositions based on hydrogen peroxide and on a basifying agent, which would be similar to oxidation dyeing.

Direct dyes also have a certain lack of light stability, associated with the poor resistance of the chromophore to photochemical attack. In addition, their sensitivity to light is dependent on the distribution of their molecules, uniformly or in aggregates, in the substrate.

Consequently, there is a real need to find direct dyes for dyeing keratin fibres, which are light-stable, and which are also resistant to bad weather, washing and perspiration and sufficiently stable in the presence of oxidizing agents such as hydrogen peroxide to be able to obtain simultaneous lightening of the fibre with the advantages outlined above, while at the same time having a toxicological profile that is compatible with cosmetic use on keratin fibres.

These aims are achieved with the present invention, one subject of which is a process for dyeing keratin fibres using direct dyes of formula (I):

salts thereof with an organic or mineral acid, geometrical isomers thereof, tautomers thereof, and solvates thereof such as the hydrates; in which formula (I):

-   -   R₁, which may be identical or different, represent:         -   a chlorine atom;         -   a (C₁-C₃)alkyl radical optionally substituted with one or             more hydroxyl groups;         -   a (C₁-C₃)alkoxy radical optionally substituted with one or             more hydroxyl groups;     -   X, which may be identical or different, represent:         -   a hydroxyl radical;         -   a radical —NR₂R₃ with R₂ and R₃ representing, independently             of each other:             -   i) a hydrogen atom;             -   ii) a C₁-C₅ alkyl radical optionally substituted with                 one or more groups chosen from hydroxyl, (C₁-C₃)alkoxy,                 amino, (C₁-C₃) alkylamino, di(C₁-C₃)alkylamino,                 aminocarbonyl, carboxylic —COOH, sulfonic —SO₃H,                 tri(C₁-C₃)alkylammonium and (C₁-C₃) alkylimidazolium;         -   a pyrrolidinyl radical optionally substituted with a group             chosen from hydroxyl, (C₁-C₃)alkoxy, amino, (C₁-C₃)             alkylamino, di(C₁-C₃)alkylamino, tri(C₁-C₃)alkylammonium and             (C₁-C₃)alkylimidazolium;     -   n represents an integer between 0 and 3 inclusive;

it being understood that when X and/or R₂ and/or R₃ comprise a cationic group, the electrical neutrality of the compounds of formula (I) is achieved with an anionic counterion or a mixture of anionic counterions that are cosmetically acceptable, for instance chlorides, bromides and sulfates.

Another subject of the invention relates to a dyeing process using reduced precursors of colourless azomethine dyes, which, once oxidized, generate the compounds of formula (I) as defined above. These precursors correspond to the compounds of formula (II):

the salts thereof with an organic or mineral acid, the geometrical isomers thereof, the tautomers thereof, and the solvates thereof such as the hydrates;

in which formula (II) R₁, X and n are as defined previously;

it being understood that:

-   -   when X and/or R₂ and/or R₃ comprise a cationic group, the         electrical neutrality of the compounds of formula (II) is         achieved with an anionic counterion or a mixture of anionic         counterions that are cosmetically acceptable, for instance         chlorides, bromides and sulfates.

Another subject of the invention is a compound of formula (I) or (II) as defined previously, it being understood that the compounds of formula (I) cannot represent compounds (1b) and (1′b):

Another subject of the invention is a dye composition for dyeing keratin fibres, comprising, in a cosmetic medium, at least one compound of formula (I) or (II) as defined previously, it being understood that the compounds of formula (I) cannot represent compounds (1b) and (1′b) as defined previously.

The direct dyes of formula (I) make it possible to overcome the drawbacks of the direct dyes conventionally used previously, and lead to dyeing results by direct dyeing that show very good resistance to light, bad weather, perspiration and rubbing. Their good stability with respect to oxidizing agents such as hydrogen peroxide also allows them to be used in a process of lightening direct dyeing.

Furthermore, it has been discovered that the reduced form of the azomethine derivatives obtained from 2-amino-3-hydroxypyridine derivatives of formula (II), used under oxidizing conditions, may also lead to colorations that show very good resistance to light, bad weather, washing, perspiration and rubbing.

For the purposes of the present invention, and unless otherwise indicated:

-   -   a “salt of an organic or mineral acid” is chosen, for example,         from a solvent derived from i) hydrochloric acid HCl, ii)         hydrobromic acid HBr, iii) sulfuric acid H₂SO₄, iv)         alkylsulfonic acids: Alk-S(O)₂OH such as methanesulfonic acid         and ethanesulfonic acid; v) arylsulfonic acids: Ar—S(O)₂OH such         as benzenesulfonic acid and toluenesulfonic acid; vi) citric         acid; vii) succinic acid; viii) tartaric acid; ix) lactic         acid; x) alkoxysulfinic acids: Alk-O—S(O)OH such as         methoxysulfinic acid and ethoxysulfinic acid; xi)         aryloxysulfinic acids such as tolueneoxysulfinic acid and         phenoxysulfinic acid; xii) phosphoric acid H₃PO₄; xiii) acetic         acid CH₃C(O)OH; xiv) triflic acid CF₃SO₃H; and xv)         tetrafluoroboric acid HBF₄;     -   an “anionic counterion” is an anion or an anionic group         associated with the cationic charge of the dye; more         particularly, the anionic counterion is chosen from: i) halides         such as chloride or bromide; ii) nitrates; iii) sulfonates,         including C₁-C₆ alkylsulfonates: Alk-S(O)₂O such as         methanesulfonate or mesylate and ethanesulfonate; iv)         arylsulfonates: Ar—S(O)₂O⁻ such as benzenesulfonate and         toluenesulfonate or tosylate; v) citrate; vi) succinate; vii)         tartrate; viii) lactate; ix) alkyl sulfates: Alk-O—S(O)O⁻ such         as methyl sulfate and ethyl sulfate; x) aryl sulfates:         Ar—O—S(O)O⁻ such as benzene sulfate and toluene sulfate; xi)         alkoxy sulfates: Alk-O—S(O)₂O⁻ such as methoxy sulfate and         ethoxy sulfate; xii) aryloxy sulfates: Ar—O—S(O)₂O⁻; xiii)         phosphate; xiv) acetate; xv) triflate; and xvi) borates such as         a tetrafluoroborate;     -   an “alkyl” radical is a saturated, linear or branched         hydrocarbon-based radical, containing from 1 to 6 carbon atoms         and particularly from 1 to 3 carbon atoms, such as the methyl or         ethyl radical;     -   an “alkoxy” radical is an “alkyl-oxy” alkyl-O-radical in which         the alkyl part is as defined previously;     -   the alkyl, alkoxy or heterocycloalkyl radicals followed by         “optionally substituted with . . . ” means that the said         radicals may have one or more hydrogen atoms replaced with one         or more substituents in question, particularly one or two         substituents in question.

One subject of the invention relates to direct dyes of formula (I) or dye precursors of formula (II).

According to a particular embodiment of the invention, the direct dyes are of formula (II).

According to another particular embodiment of the invention, the direct dyes are of formula (I).

One particular embodiment of the invention concerns compounds of formula (I) or (II) for which n is zero.

According to another particular embodiment of the invention, the compound(s) of formula (I) or (II) contained in the composition according to the invention is (are) such that n is 1 and R₁ represents a (C₁-C₃) alkyl group such as methyl.

One variant concerns compounds of formula (I) or (II) for which X represents a hydroxyl radical.

Another variant of the invention involves compounds of formula (I) or (II) for which X represents a radical —NR₂R₃ with R₂ and R₃ representing, independently of each other, i) a hydrogen atom or ii) a C₁-C₅ alkyl radical optionally substituted with one or more groups chosen from hydroxyl, (C₁-C₃)alkoxy, amino, (C₁-C₃)alkylamino, di(C₁-C₃)alkylamino, aminocarbonyl, carboxylic —COOH, sulfonic —SO₃H, tri(C₁-C₃)alkyl-ammonium and (C₁-C₃)alkylimidazolium. More particularly, X represents a group chosen from: i) (di) (C₁-C₃) (alkyl)amino; ii) (di) [hydroxy(C₁-C₃)alkyl]amino; iii) (C₁-C₃)akylimidazolium(C₁-C₃)alkylamino; iv) [N—(C₁-C₃)alkyl,N-(C₁-C₃)akylimidazolium(C₁-C₃)alkyl]amino; v) tri(C₁-C₃)alkylammonium(C₁-C₅)alkylamino and vi) (di) [tri (C₁-C₃) alkylammonium (C₁-C₅)alkyl]amino.

According to another particular embodiment of the invention, the compounds of formula (I) or (II) are such that X represents a pyrrolidinyl group optionally substituted with a tri(C₁-C₃)alkylammonium or (C₁-C₃)alkylimidazolium group. More particularly, X represents a pyrrolidino radical optionally substituted with a tri(C₁-C₃)alkylammonium or (C₁-C₃)alkyl-imidazolium group.

As examples of compounds of formula (I) or (II) contained in the composition according to the invention, mention may be made of the dyes (1a) to (1j) and precursors (2a) to (2j) below, and also the salts thereof with an organic or mineral acid, geometrical isomers thereof, tautomers thereof and solvates thereof such as the hydrates:

Dyes of Formula (I):

2-Amino-5-(4-hydroxyphenyl- amino)-6-(4-hydroxyphenyl- imino)-6H-pyridin-3-one

2-Amino-5-(4-aminomethylphenyl- amino)-6-(4-aminomethylphenyl- imino)-6H-pyridin-3-one

2-Amino-5-{4-[bis(2-hydroxy- ethyl)amino]phenylamino}-6-{4- [bis(2-hydroxyethyl)amino]- phenylimino}-6H-pyridin-3-one

Salt of 1-{3-[(4-{[6-amino-3- [(4-{[3-(3-methyl-1H-imidazol- 3-ium- 1-yl)propyl]amino}phenyl)amino]- 5-oxopyridin-2(5H)ylidene]- amino}phenyl)amino]propyl}- 3-methyl-1H-imidazol-3-ium

Salt of 1-(4-{[6-amino-5-oxo-3- ({4-[3- (trimethylammonio)pyrrolidin- 1-yl]phenyl}amino)pyridin- 2(5H)ylidene]amino}phenyl)- N,N,N-trimethylpyrrolidin- 3-aminium

Salt of 1-[1-(4-{[6-amino-3- ({4-[3-(3-methyl-1H-imidazol-3- ium-1-yl)pyrrolidin-1- yl]phenyl}amino)-5-oxopyridin- 2(5H)- ylidene]amino}phenyl)pyrrolidin- 3-yl]-3-methyl-1H-imidazol- 3-ium

Salt of 1-{2-[(4-{[6-amino-3- [(4-{ethyl[2-(3-methyl-1H- imidazol-3-ium-1- yl)ethyl]amino}phenyl)amino]-5- oxopyridin-2(5H) - ylidene]amino}phenyl) (ethyl)- amino]ethyl}-3-methyl-1H- imidazol-3-ium

Salt of 3-[(4-{[6-amino-5-oxo- 3-[(4-{[3- (trimethylammonio)propyl]- amino}phenyl)amino]pyridin- 2(5H)ylidene]amino}phenyl)- amino]-N,N,N-trimethylpropan- 1-aminium

Salt of 3-{(4-{[6-amino-3-[(4- {bis[3- (trimethylammonio)propyl]- amino}phenyl)amino]-5-oxo- pyridin-2(5H)ylidene]amino}- phenyl) [3-(trimethylammonio)- propyl]amino}-N,N,N-trimethyl- propan-1-aminium Dye precursors of Formula (II):

2-Amino-5,6-bis(4-hydroxy- phenylamino)pyridin-3-ol

2-Amino-5,6-bis(4-aminophenyl- amino)pyridin-3-ol

2-Amino-5,6-bis(4-aminomethyl- phenylamino)pyridin-3-ol

2-Amino-5,6-bis{4- [bis(2-hydroxyethyl)amino]- phenylamino}pyridin-3-ol

Salt of 1,1′-[(6-amino- 5-hydroxypyridine- 2,3-diyl)bis(imino- 4,1-phenyleneiminopropane- 3,1-diyl)]bis(3-methyl-1H- imidazol-3-ium)

Salt of 1,1′-[(6-amino- 5-hydroxypyridine- 2,3-diyl)bis(imino- 4,1-phenylene)]bis(N,N,N- trimethylpyrrolidin-3-aminium)

Salt of 1,1′-[(6-amino- 5-hydroxypyridine-2,3- diyl)bis(imino-4,1- phenylenepyrrolidine-1,3- diyl)]bis(3-methyl-1H-imidazol- 3-ium)

Salt of 1,1′-{(6-amino-5- hydroxypyridine-2,3- diyl)bis[imino-4,1- phenylene(ethylimino)ethane- 2,1-diyl]}bis(3-methyl-1H- imidazol-3-ium)

Salt of 3,3′-[(6-amino- 5-hydroxypyridine-2,3- diyl)bis(imino-4,1- phenyleneimino)]bis(N,N,N- trimethylpropan-1-aminium)

Salt of 3,3′,3″,3′′′- [(6-amino-5-hydroxypyridine- 2,3-diyl)bis(imino- 4,1-phenylene- nitrilo)]tetrakis(N,N,N- trimethylpropan-1-aminium) with An⁻, which may be identical or different, representing an anionic counterion such as halide, An⁻ particularly representing a chloride.

More particularly, the dyes that are contained in the composition are chosen from the preceding dyes (1a), (1b), (1c), (1d), (1f), (1g) and (1i), and the dye precursors are chosen from the preceding precursors (2a), (2b), (2c) and (2d) and the salts thereof with an organic or mineral acid, geometrical isomers thereof, tautomers thereof, and solvates thereof such as hydrates.

The compounds of formula (I) or (II) of the invention are prepared according to the following general synthetic routes:

1—Access to the Compounds Corresponding to Formula (I):

The compounds corresponding to formula (I) are generally obtained by reacting 2-amino-3-hydroxypyridine with a para-aminophenol derivative (X═OH) or a para-phenylenediamine derivative (X═—NR₂R₃), preferably in basic medium in the presence of an oxidizing agent. The base used is preferentially an aqueous solution of ammonia or of sodium hydroxide and the oxidizing agent is preferentially chosen from hydrogen peroxide, potassium ferricyanide, air, ammonium persulfate and manganese oxide.

Similar synthetic approaches are described in patents FR 2 234 277, FR 2 047 932, FR 2 106 661 and FR 2 121 101.

2—Access to the Compounds Corresponding to Formula (II):

The compounds corresponding to formula (II) are generally obtained by reacting the compounds of formula (I) with a reducing agent. This reducing agent preferentially is sodium hydrosulfite.

Similar synthetic approaches are described in patents FR 2 056 799, FR 2 047 932, FR 2 165 965 and FR 2 262 023.

Another subject of the invention is a dye composition for dyeing keratin fibres, comprising, in a cosmetic medium, at least one compound of formula (I) or (II) as defined previously.

One subject of the invention relates to a cosmetically acceptable composition for dyeing keratin fibres, especially human keratin fibres such as the hair, comprising at least one direct dye of formula (I) or a dye precursor of formula (II).

The dye composition that is useful in the invention generally contains an amount of dye of formula (I) or of precursor of formula (II) of between 0.001% and 30% relative to the total weight of the composition. Preferably, this amount is between 0.005% and 10% by weight and even more preferentially between 0.01% and 6% by weight relative to the total weight of the composition.

The dye composition containing the dye of formula (I) or the precursor of formula (II), in particular the precursor of formula (II), may also contain an oxidizing agent such as hydrogen peroxide, urea peroxide, alkali metal bromates, persalts, peracids and oxidase enzymes.

The dye composition may also contain additional direct dyes. These direct dyes are chosen, for example, from neutral, acidic or cationic nitrobenzene direct dyes, neutral, acidic or cationic azo direct dyes, tetraazapentamethine dyes, neutral, acidic or cationic quinone and in particular anthraquinone dyes, azine direct dyes, triarylmethane direct dyes, indoamine direct dyes and natural direct dyes.

Among the nitrobenzene direct dyes that may be mentioned, in a non-limiting manner, are the following compounds:

-   1,4-diamino-2-nitrobenzene,     1-amino-2-nitro-4-β-hydroxyethylaminobenzene,     1-amino-2-nitro-4-bis(β-hydroxyethyl)aminobenzene,     1,4-bis(β-hydroxyethyl-amino)-2-nitrobenzene,     1-β-hydroxyethylamino-2-nitro-4-bis(β-hydroxyethylamino)benzene,     1-β-hydroxyethylamino-2-nitro-4-aminobenzene,     1-β-hydroxyethylamino-2-nitro-4-(ethyl)(β-hydroxyethyl)aminobenzene,     1-amino-3-methyl-4-β-hydroxyethylamino-6-nitrobenzene,     1-amino-2-nitro-4-β-hydroxyethylamino-5-chlorobenzene,     1,2-diamino-4-nitrobenzene,     1-amino-2-β-hydroxyethylamino-5-nitrobenzene,     1,2-bis(β-hydroxyethylamino)-4-nitro-benzene,     1-amino-2-tris(hydroxymethyl)methylamino-5-nitrobenzene,     1-hydroxy-2-amino-5-nitrobenzene, 1-hydroxy-2-amino-4-nitrobenzene,     1-hydroxy-3-nitro-4-aminobenzene,     1-hydroxy-2-amino-4,6-dinitrobenzene,     1-β-hydroxyethyloxy-2-β-hydroxyethylamino-5-nitrobenzene,     1-methoxy-2-β-hydroxyethylamino-5-nitrobenzene,     1-β-hydroxyethyloxy-3-methylamino-4-nitrobenzene,     1-β,γ-dihydroxypropyloxy-3-methylamino-4-nitrobenzene,     1-β-hydroxyethylamino-4-β,γ-dihydroxypropyloxy-2-nitro-benzene,     1-β,γ-dihydroxypropylamino-4-trifluoromethyl-2-nitrobenzene,     1-β-hydroxyethylamino-4-trifluoro-methyl-2-nitrobenzene,     1-β-hydroxyethylamino-3-methyl-2-nitrobenzene,     1-β-aminoethylamino-5-methoxy-2-nitro-benzene,     1-hydroxy-2-chloro-6-ethylamino-4-nitro-benzene,     1-hydroxy-2-chloro-6-amino-4-nitrobenzene,     1-hydroxy-6-bis(β-hydroxyethyl)amino-3-nitrobenzene,     1-β-hydroxyethylamino-2-nitrobenzene,     1-hydroxy-4-β-hydroxyethylamino-3-nitrobenzene.

Among the azo direct dyes, mention may be made of the cationic azo dyes described in patent applications WO-95/15144, WO-95/01772 and EP-714 954, the content of which forms an integral part of the invention.

Among these compounds, mention may be made most particularly of the following dyes: 1,3-dimethyl-2-[[4-(dimethylamino)phenyl]azo]-1H-imidazolium chloride, 1,3-dimethyl-2-[(4-aminophenyl)azo]-1H-imidazolium chloride, 1-methyl-4-[(methylphenylhydrazono)methyl]-pyridinium methyl sulfonate.

Among the azo direct dyes, mention may also be made of the following dyes, described in the COLOUR INDEX INTERNATIONAL 3rd edition:

-   Disperse Red 17, Acid Yellow 9, Acid Black 1, Basic Red 22, Basic     Red 76, Basic Yellow 57, Basic Brown 16, Acid Yellow 36, Acid Orange     7, Acid Red 33, Acid Red 35, Basic Brown 17, Acid Yellow 23, Acid     Orange 24, Disperse Black 9.

Mention may also be made of 1-(4′-aminodiphenylazo)-2-methyl-4-bis(β-hydroxyethyl)aminobenzene and 4-hydroxy-3-(2-methoxyphenylazo)-1-naphthalenesulfonic acid.

Among the quinone direct dyes, mention may be made of the following dyes:

-   Disperse Red 15, Solvent Violet 13, Acid Violet 43, Disperse Violet     1, Disperse Violet 4, Disperse Blue 1, Disperse Violet 8, Disperse     Blue 3, Disperse Red 11, Acid Blue 62, Disperse Blue 7, Basic Blue     22, Disperse Violet 15, Basic Blue 99, and also the following     compounds: 1-N-methylmorpholiniumpropylamino-4-hydroxyanthraquinone,     1-aminopropylamino-4-methylaminoanthraquinone,     1-aminopropylaminoanthraquinone,     5-β-hydroxy-ethyl-1,4-diaminoanthraquinone,     2-aminoethylamino-anthraquinone,     1,4-bis(β,γ-dihydroxypropylamino)-anthraquinone.

Among the azine dyes, mention may be made of the following compounds:

-   -   Basic Blue 17 and Basic Red 2.

Among the triarylmethane dyes, mention may be made of the following compounds: Basic Green 1, Acid Blue 9,

Basic Violet 3, Basic Violet 14, Basic Blue 7, Acid Violet 49, Basic Blue 26, Acid Blue 7.

Among the indoamine dyes, mention may be made of the following compounds:

-   -   2-β-hydroxyethlyamino-5-[bis(β-4′-hydroxyethyl)amino]-anilino-1,4-benzoquinone;     -   2-β-hydroxyethylamino-5-(2′-methoxy-4′-amino)anilino-1,4-benzoquinone;     -   3-N-(2′-chloro-4′-hydroxy)phenylacetylamino-6-methoxy-1,4-benzoquinoneimine;     -   3-N-(3′-chloro-4′-methylamino)phenylureido-6-methyl-1,4-benzoquinoneimine;     -   3-[4′-N-(ethyl,carbamylmethyl)amino]phenylureido-6-methyl-1,4-benzoquinoneimine.

Among the natural direct dyes, mention may be made of lawsone, juglone, alizarin, purpurin, carminic acid, kermesic acid, purpurogallin, protocatechaldehyde, indigo, isatin, curcumin, spinulosin and apigenidin. Extracts or decoctions containing these natural dyes, and especially henna-based poultices or extracts, may also be used.

The dye composition may contain one or more oxidation bases and/or one or more couplers conventionally used for the dyeing of keratin fibres.

Among the oxidation bases, mention may be made of para-phenylenediamines, bis(phenyl)alkylenediamines, para-aminophenols, bis-para-aminophenols, ortho-aminophenols and heterocyclic bases, and the addition salts thereof.

Among the couplers, mention may be made especially of meta-phenylenediamines, meta-aminophenols, meta-diphenols, naphthalene-based couplers and heterocyclic couplers, and the addition salts thereof.

The coupler(s) is (are) each generally present in an amount of between 0.001% and 10% by weight and preferably between 0.005% and 6% by weight relative to the total weight of the dye composition.

The oxidation base(s) present in the dye composition is (are) each generally present in an amount of between 0.001% and 10% by weight and preferably between 0.005% and 6% by weight relative to the total weight of the dye composition.

In general, the addition salts of the oxidation bases and couplers used in the context of the invention are especially chosen from the salts of addition with an acid, such as the hydrochlorides, hydrobromides, sulfates, citrates, succinates, tartrates, lactates, tosylates, benzenesulfonates, phosphates and acetates, and the salts of addition with a base, such as alkali metal hydroxides, for instance sodium hydroxide, potassium hydroxide, ammonia, amines or alkanolamines.

The medium that is suitable for dyeing, also known as the dye support, is a cosmetic medium generally comprising water or a mixture of water and of at least one organic solvent. Examples of organic solvents that may be mentioned include lower C₁-C₄ alkanols, such as ethanol and isopropanol; polyols and polyol ethers, for instance 2-butoxyethanol, propylene glycol, propylene glycol monomethyl ether and diethylene glycol monomethyl ether and monomethyl ether, and also aromatic alcohols, for instance benzyl alcohol or phenoxyethanol, and mixtures thereof.

When they are present, the solvents are preferably present in proportions preferably of between 1% and 40% by weight approximately, and even more preferentially between 5% and 30% by weight approximately, relative to the total weight of the dye composition.

The dye composition may also contain various adjuvants conventionally used in hair dye compositions, such as anionic, cationic, nonionic, amphoteric or zwitterionic surfactants or mixtures thereof, anionic, cationic, nonionic, amphoteric or zwitterionic polymers or mixtures thereof, mineral or organic thickeners, and in particular anionic, cationic, nonionic and amphoteric polymeric associative thickeners, antioxidants, penetrants, sequestrants, fragrances, buffers, dispersants, conditioning agents, for instance volatile or non-volatile, modified or unmodified silicones such as amino silicones, film-forming agents, ceramides, preserving agents, opacifiers and conductive polymers.

The above adjuvants are generally present in an amount for each of them of between 0.01% and 20% by weight relative to the weight of the composition.

Needless to say, a person skilled in the art will take care to select this or these optional additional compounds such that the advantageous properties intrinsically associated with the dye composition in accordance with the invention are not, or are not substantially, adversely affected by the envisaged addition(s).

The pH of the dye composition is generally between 3 and 14 approximately, and preferably between 5 and 12 approximately. It may be adjusted to the desired value by means of acidifying or basifying agents usually used in the dyeing of keratin fibres, or alternatively using standard buffer systems.

According to one particular mode of the invention, when the dye composition comprises at least one dye of formula (I), the composition has a pH of between 6 and 11. According to another particular mode of the invention, when the composition comprises at least one dye precursor of formula (II), the composition has pH of between 6 and 11.

Among the acidifying agents, examples that may be mentioned include mineral or organic acids, for instance hydrochloric acid, orthophosphoric acid, sulfuric acid, carboxylic acids, for instance acetic acid, tartaric acid, citric acid or lactic acid, and sulfonic acids.

Among the basifying agents, examples that may be mentioned include aqueous ammonia, alkali metal carbonates, alkanolamines such as monoethanolamine, diethanolamine and triethanolamine, and also derivatives thereof, sodium hydroxide, potassium hydroxide and the compounds of formula (γ) below:

in which W_(a) is a propylene residue optionally substituted with a hydroxyl group or a C₁-C₄ alkyl radical; R_(a1), R_(a2), R_(a3) and R_(a4), which may be identical or different, represent a hydrogen atom or a C₁-C₄ alkyl or C₁-C₄ hydroxyalkyl radical.

The dye composition may be in various forms, such as in the form of a liquid, a cream or gel, or in any other form that is suitable for dyeing keratin fibres, and especially the hair.

Another subject of the invention is a process for dyeing keratin fibres, in particular the hair, which consists in applying to keratin materials, in the presence or absence of an oxidizing agent, a dye composition comprising, in a cosmetic medium, at least one azomethine dye of formula (I) or a dye precursor of formula (II) as defined previously.

After a leave-in time, the keratin fibres are rinsed to reveal dyed fibres. The leave-in time is generally between 3 and 50 minutes approximately and preferably 5 to 40 minutes approximately.

The application of the dye composition according to the invention is generally performed at room temperature. However, it may be performed at temperatures ranging from 20 to 80° C.

The examples that follow serve to illustrate the invention without, however, being limiting in nature. The dyes of the examples below were fully characterized via the standard spectroscopic and spectrometric methods.

EXAMPLES Examples of Synthesis Example 1 Synthesis of 2-amino-5-(4-hydroxyphenyl-amino)-6-(4-hydroxyphenylimino)-6H-pyridin-3-one (compound (1a))

5.5 g (0.05 mol) of 2-amino-3-hydroxypyridine, 5.5 g (0.05 mol) of 4-aminophenol, 50 ml of ethanol, 25 ml of water, 50 g of aqueous 20% NH₄OH solution and 50 g of a 30% aqueous hydrogen peroxide solution (110 volumes) are respectively added to a round-bottomed flask, with stirring. The reaction medium is stirred for 4 hours at room temperature and then for 25 hours at 60° C.

After cooling to room temperature, the solid formed is filtered off, washed with petroleum ether and then dried under vacuum over P₂O₅. 4.8 g of 2-amino-5-(4-hydroxyphenylamino)-6-(4-hydroxyphenylimino)-6H-pyridin-3-one of formula (1a) are obtained, in the form of a red solid.

Example 2 Synthesis of 2-amino-5-(4-aminophenyl-amino)-6-(4-aminophenylimino)-6H-pyridin-3-one 2 (compound (1b))

5.5 g (0.05 mol) of 2-amino-3-hydroxypyridine, 10.8 g (0.1 mol) of para-phenylenediamine, 50 ml of ethanol, 25 ml of water, 50 g of aqueous 20% NH₄OH solution and 50 g of a 30% aqueous hydrogen peroxide solution (110 volumes) are respectively added to a round-bottomed flask, with stirring. The reaction medium is stirred for 7 hours at room temperature and then for 15 hours at 38° C.

After cooling to room temperature, the solid formed is filtered off, washed with petroleum ether and then dried under vacuum over P₂O₅. 11 g of 2-amino-5-(4-aminophenylamino)-6-(4-aminophenylimino)-6H-pyridin-3-one of formula (1b) are obtained.

Example 3 Synthesis of 2-amino-5-(4-aminomethyl-phenylamino)-6-(4-aminomethylphenylimino)-6H-pyridin-3-one 3 (compound (1c))

5.5 g (0.05 mol) of 2-amino-3-hydroxypyridine and 19.5 g (0.1 mol) of para-toluenediamine are introduced into 50 ml of ethanol and 25 ml of water. 50 g of aqueous 20% NH₄OH solution and 50 g of a 30% aqueous hydrogen peroxide solution (110 volumes) are then added. The reaction medium is heated at 37° C. for 6 hours 30 minutes with stirring.

After cooling to room temperature, the solid formed is filtered off and washed with petroleum ether. The crude product obtained is then purified by chromatography on a column of silica (eluent: gradient ranging from CH₂Cl₂ to a CH₂Cl₂/MeOH mixture) to give 100 mg of 2-amino-5-(4-aminomethylphenylamino)-6-(4-aminomethylphenyl-imino)-6H-pyridin-3-one of formula (1c).

Example 4 Synthesis of 2-amino-5-{4-[bis(2-hydroxy-ethyl)amino]phenylamino}-6-{4-[bis-(2-hydroxyethyl)amino]phenylimino}-6H-pyridin-3-one 4 (compound (1d))

0.55 g (0.005 mol) of 2-amino-3-hydroxypyridine and 1.96 g (0.005 mol) of 2-[(4-aminophenyl)-(2-hydroxy-ethyl)amino]ethanol are introduced into 5 ml of ethanol and 2.5 ml of water. 5 g of aqueous 20% NH₄OH solution and 5 g of a 30% aqueous hydrogen peroxide solution (110 volumes) are then added. The reaction medium is stirred at room temperature for 18 hours.

40 ml of water are added and the solid formed is then filtered off and washed with water.

After drying under vacuum over P₂O₅, 0.42 g of 2-amino-5-{4-[bis(2-hydroxyethyl)amino]phenylamino}-6-{4-[bis(2-hydroxyethyl)amino]phenylimino}-6H-pyridin-3-one of formula (1d) is obtained.

Example 5 Synthesis of 3-amino-5,6-bis[(4-amino-phenyl)amino]pyridin-2-ol (compound (2b))

10 mg (0.03 mol) of 2-amino-5-[(4-aminophenyl)amino]-6-[(4-aminophenyl)imino]pyridin-3(6H)one are added to a solution containing 13.5 mg of sodium hydrosulfite in 250 μl of methanol and 5 μl of an aqueous sodium hydroxide solution. The reaction medium is stirred and the solution is then worked up according to the usual procedure and characterized. 3-Amino-5,6-bis[(4-aminophenyl)amino]pyridin-2-ol (2b) is obtained.

Example 6 Synthesis of 3-amino-5,6-bis[(4-hydroxy-phenyl)amino]pyridin-2-ol (compound (2a))

10 mg (0.04 mol) of 2-amino-5-[(4-hydroxyphenyl)amino]-6-[(4-hydroxyphenyl)imino]pyridin-3(6H) one are added to a solution containing 13.5 mg of sodium hydrosulfite in 250 μl of methanol and 5 μl of an aqueous sodium hydroxide solution. The reaction medium is stirred and the solution is then worked up according to the usual procedure and characterized. 3-Amino-5,6-bis-[(4-hydroxyphenyl)amino]pyridin-2-ol (2a) is obtained.

Example 7 Synthesis of 3-amino-5,6-bis({4-[bis-(2-hydroxyethyl)amino]phenyl}amino)pyridin-2-ol (compound 2d))

15 mg (0.04 mol) of (6Z)-2-amino-5-({4-[bis(2-hydroxy-ethyl)amino]phenyl}amino)-6-({4-[bis(2-hydroxyethyl)-amino]phenyl}imino)pyridin-3(6H) one are added to a solution containing 13.5 mg of sodium hydrosulfite in 250 μl of methanol and 5 μl of an aqueous sodium hydroxide solution. The reaction medium is stirred and the solution is then worked up according to the usual procedure and characterized. 3-Amino-5,6-bis({4-[bis(2-hydroxyethyl)amino]phenyl}amino)pyridin-2-ol (2d) is obtained.

Example of Dyeing Dyeing in Neutral Medium

The dye composition (A) below is prepared using compound (1a) synthesized previously.

Composition (A) Compound (1a) 10⁻³ mol Dye support (1) (*) Demineralized 100 g water qs (*): dye support (1) pH = 7 with the dye support constituted of: 96° ethyl alcohol 20.8 g Pentasodium salt of diethylenetriaminepenta- 0.48 g AM acetic acid as an aqueous 40% solution C₈-C₁₀ alkyl polyglucoside as an aqueous 60% 3.6 g AM solution Benzyl alcohol 2.0 g Polyethylene glycol containing 8 units of 3.0 g ethylene oxide Na₂HPO₄ 0.28 g KH₂PO₄ 0.46 g

Composition (A) is applied to locks of grey hair containing 90% white hairs. After a leave-on time of 30 minutes, the locks are rinsed, washed with a standard shampoo, rinsed again and then dried.

The shade obtained is given in the table below:

Composition (A) Shade observed after treatment orange 

1. Compound of formula (I) or (II):

salts thereof with an organic or mineral acid, geometrical isomers thereof, tautomers thereof, and solvates thereof such as the hydrates; in which formulae (I) and (II): R₁, which may be identical or different, represent: a chlorine atom; a (C₁-C₃)alkyl radical optionally substituted with one or more hydroxyl groups; a (C₁-C₃)alkoxy radical optionally substituted with one or more hydroxyl groups; X, which may be identical or different, represent: a hydroxyl radical; a radical —NR₂R₃ with R₂ and R₃ representing, independently of each other: i) a hydrogen atom; ii) a C₁-C₅ alkyl radical optionally substituted with one or more groups chosen from hydroxyl, (C₁-C₃)alkoxy, amino, (C₁-C₃) alkylamino, di(C₁-C₃)alkylamino, aminocarbonyl, carboxylic —COOH, sulfonic —SO₃H, tri(C₁-C₃)alkylammonium and (C₁-C₃) alkylimidazolium; a pyrrolidinyl radical optionally substituted with a group chosen from hydroxyl, (C₁-C₃)alkoxy, amino, (C₁-C₃)alkylamino, di(C₁-C₃)alkylamino, tri(C₁-C₃)alkylammonium and (C₁-C₃) alkylimidazolium; n represents an integer between 0 and 3 inclusive; it being understood that when X and/or R₂ and/or R₃ comprise a cationic group, the electrical neutrality of the compound of formula (I) or (II) is achieved with an anionic counterion or a mixture of anionic counterions that are cosmetically acceptable, and the compounds of formula (I) cannot represent compounds (1b) and (1′b):


2. Compound of formula (I) or (II) according to claim 1, such that n is equal to zero.
 3. Compound of formula (I) or (II) according to claim 1, such that when n is 1, R₁ represents a (C₁-C₃)alkyl radical.
 4. Compound of formula (I) or (II) according to any one of the preceding claims, for which X represents a hydroxyl radical.
 5. Compound of formula (I) or (II) according to any one of claims 1 to 3, for which X represents a radical —NR₂R₃ with R₂ and R₃ representing, independently of each other, i) a hydrogen atom or ii) a C₁-C₅ alkyl radical optionally substituted with one or more groups chosen from hydroxyl, (C₁-C₃)alkoxy, amino, (C₁-C₃)alkyl-amino, di(C₁-C₃)alkylamino, aminocarbonyl, carboxylic —COOH, sulfonic —SO₃H, tri(C₁-C₃)alkylammonium and (C₁-C₃) alkylimidazolium.
 6. Compound of formula (I) or (II) according to any one of claims 1 to 3, for which X represents a pyrrolidinyl group optionally substituted with a tri(C₁-C₃)alkylammonium or (C₁-C₃)alkylimidazolium group.
 7. Compound of formula (I) or (II) according to any one of the preceding claims, chosen from:

2-Amino-5-(4-hydroxyphenyl- amino)-6-(4-hydroxyphenyl- imino)-6H-pyridin-3-one

2-Amino-5-(4-aminomethylphenyl- amino)-6-(4-aminomethylphenyl- imino)-6H-pyridin-3-one

2-Amino-5-{4-[bis(2-hydroxy- ethyl)amino]phenylamino}-6-{4- [bis(2-hydroxyethyl)amino]- phenylimino}-6H-pyridin-3-one

Salt of 1-{3-[(4-{[6-amino-3- [(4-{[3-(3-methyl-1H-imidazol- 3-ium- 1-yl)propyl]amino}phenyl)amino]- 5-oxopyridin-2(5H)ylidene]- amino}phenyl)amino]propyl}- 3-methyl-1H-imidazol-3-ium

Salt of 1-(4-{[6-amino-5-oxo-3- ({4-[3- (trimethylammonio)pyrrolidin- 1-yl]phenyl}amino)pyridin- 2(5H)ylidene]amino}phenyl)- N,N,N-trimethylpyrrolidin- 3-aminium

Salt of 1-[1-(4-{[6-amino-3- ({4-[3-(3-methyl-1H-imidazol-3- ium-1-yl)pyrrolidin-1- yl]phenyl}amino)-5-oxopyridin- 2(5H)- ylidene]amino}phenyl)pyrrolidin- 3-yl]-3-methyl-1H-imidazol- 3-ium

Salt of 1-{2-[(4-{[6-amino-3- [(4-{ethyl[2-(3-methyl-1H- imidazol-3-ium-1- yl)ethyl]amino}phenyl)amino]-5- oxopyridin-2(5H) - ylidene]amino}phenyl) (ethyl)- amino]ethyl}-3-methyl-1H- imidazol-3-ium

Salt of 3-[(4-{[6-amino-5-oxo- 3-[(4-{[3- (trimethylammonio)propyl]- amino}phenyl)amino]pyridin- 2(5H)ylidene]amino}phenyl)- amino]-N,N,N-trimethylpropan- 1-aminium

Salt of 3-{(4-{[6-amino-3-[(4- {bis[3- (trimethylammonio)propyl]- amino}phenyl)amino]-5-oxo- pyridin-2(5H)ylidene]amino}- phenyl) [3-(trimethylammonio)- propyl]amino}-N,N,N-trimethyl- propan-1-aminium

2-Amino-5,6-bis(4-hydroxy- phenylamino)pyridin-3-ol

2-Amino-5,6-bis (4-aminophenyl- amino)pyridin-3-ol

2-Amino-5,6-bis(4-aminomethyl- phenylamino)pyridin-3-ol

2-Amino-5,6-bis{4- [bis(2-hydroxyethyl)amino]- phenylamino}pyridin-3-ol

Salt of 1,1′-[(6-amino- 5-hydroxypyridine- 2,3-diyl)bis(imino- 4,1-phenyleneiminopropane- 3,1-diyl)]bis(3-methyl-1H- imidazol-3-ium)

Salt of 1,1′-[(6-amino- 5-hydroxypyridine- 2,3-diyl)bis(imino- 4,1-phenylene)]bis(N,N,N- trimethylpyrrolidin-3-aminium)

Salt of 1,1′-[(6-amino- 5-hydroxypyridine-2,3- diyl)bis(imino-4,1- phenylenepyrrolidine-1,3- diyl)]bis(3-methyl-1H-imidazol- 3-ium)

Salt of 1,1′-{(6-amino-5- hydroxypyridine-2,3- diyl)bis[imino-4,1- phenylene(ethylimino)ethane- 2,1-diyl]}bis(3-methyl-1H- imidazol-3-ium)

Salt of 3,3′-[(6-amino- 5-hydroxypyridine-2,3- diyl)bis(imino-4,1- phenyleneimino)]bis(N,N,N- trimethylpropan-1-aminium)

Salt of 3,3′,3″,3′′′- [(6-amino-5-hydroxypyridine- 2,3-diyl)bis(imino- 4,1-phenylene- nitrilo)]tetrakis(N,N,N- trimethylpropan-1-aminium)

with An⁻, which may be identical or different, representing an anionic counterion.
 8. Dye composition for dyeing keratin fibres, comprising, in a cosmetic medium, at least one compound of formula (I) or (II) as defined in any one of claims 1 to
 7. 9. Composition according to the preceding claim, in which the compound of formula (I) or (II) is present in an amount of between 0.001% and 30% by weight relative to the total weight of the composition.
 10. Composition according to either of claims 8 and 9, in which, when the composition comprises at least one compound of formula (I), the composition has a pH of between 6 and
 11. 11. Composition according to either of claims 8 and 9, in which, when the composition comprises at least one compound of formula (II), the composition has a pH of between 6 and
 11. 12. Composition according to any one of claims 8 to 11, which also comprises at least one oxidizing agent.
 13. Composition according to the preceding claim, in which the oxidizing agent is chosen from hydrogen peroxide, urea peroxide, alkali metal bromates, persalts, peracids and oxidase enzymes.
 14. Process for dyeing keratin fibres, in which a suitable dye composition comprising at least one compound of formula (I) or (II):

salts thereof with an organic or mineral acid, geometrical isomers thereof, tautomers thereof, and solvates thereof such as the hydrates; in which formulae (I) and (II): R₁, which may be identical or different, represent: a chlorine atom; a (C₁-C₃)alkyl radical optionally substituted with one or more hydroxyl groups; a (C₁-C₃)alkoxy radical optionally substituted with one or more hydroxyl groups; X, which may be identical or different, represent: a hydroxyl radical; a radical —NR₂R₃ with R₂ and R₃ representing, independently of each other: i) a hydrogen atom; ii) a C₁-C₅ alkyl radical optionally substituted with one or more groups chosen from hydroxyl, (C₁-C₃)alkoxy, amino, (C₁-C₃) alkylamino, di(C₁-C₃)alkylamino, aminocarbonyl, carboxylic —COOH, sulfonic —SO₃H, tri(C₁-C₃)alkylammonium and (C₁-C₃) alkylimidazolium; a pyrrolidinyl radical optionally substituted with a group chosen from hydroxyl, (C₁-C₃)alkoxy, amino, (C₁-C₃)alkylamino, di(C₁-C₃)alkylamino, tri(C₁-C₃)alkylammonium and (C₁-C₃) alkylimidazolium; n represents an integer between 0 and 3 inclusive; it being understood that when X and/or R₂ and/or R₃ comprise a cationic group, the electrical neutrality of the compound of formula (I) or (II) is achieved with an anionic counterion or a mixture of anionic counterions that are cosmetically acceptable, is applied to keratin materials.
 15. Process for dyeing keratin fibres according to the preceding claim, in which a suitable dye composition as defined in any one of claims 8 to 13 is applied to keratin materials.
 16. Use of a compound of formula (I) or (II) as defined in any one of claims 1 to 7, for dyeing keratin fibres. 